Neuropsychologia
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Comparative Study
Receptive amusia: temporal auditory processing deficit in a professional musician following a left temporo-parietal lesion.
This study examined the musical processing in a professional musician who suffered from amusia after a left temporo-parietal stroke. The patient showed preserved metric judgement and normal performance in all aspects of melodic processing. By contrast, he lost the ability to discriminate or reproduce rhythms. ⋯ Since rhythm processing was selectively disturbed in the auditory modality, the arrhythmia cannot be attributed to a impairment of supra-modal temporal processing. Rather, our findings suggest modality-specific encoding of musical temporal information. Besides, it is proposed that the processing of auditory rhythmic sequences involves a specific left hemispheric temporal buffer.
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Comparative Study Clinical Trial
Convergent and divergent effects of neck proprioceptive and visual motion stimulation on visual space processing in neglect.
Visual motion stimulation as well as neck muscle vibration are known to effectively modulate the subjective body orientation in spatial neglect. However, so far only motion stimulation has been demonstrated to substantially influence size and space distortion in neglect patients. The present study aimed to compare the two stimulation methods with respect to their potentially differential impact on subjective body orientation and on space and size distortion, in five neglect patients showing perceptual distortions. ⋯ Additionally, left motion stimulation significantly ameliorated the leftward overextension in size matching, line bisection and distance estimation in all five patients. In contrast, during neck vibration only two patients showed an improvement for line bisection and size estimation and none did so for distance estimation. Since these two patients differed from the others as they had either no visual field defects or a major visual field sparing, we suggest--based on recent anatomical and neuropsychological findings--that neck vibration only tends to improve pure neglect-related visuo-perceptual distortions whereas motion stimulation can additionally improve perceptual distortions in neglect associated with hemianopia.
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Comparative Study
Simulating unilateral neglect in normals using prism adaptation: implications for theory.
Rightward deviation on line bisection is considered one of the most classic clinical signs of unilateral visual neglect--a cognitive disorder of spatial processing that commonly follows right brain damage. Recently, short-term adaptation to wedge prisms has been shown to significantly reduce neglect on this and other conventional diagnostic tasks. Our previous study has shown that visuomotor adaptation in normals produces a similar pattern of directional bias on a line bisection task. ⋯ A final experiment confirmed that these after-effects are specific to prism adaptation rather than passive prism exposure. Collectively, these findings confirm that adaptation to left-deviating prisms in normals produces a reliable right-sided bias and as shown by a previous visuospatial judgement task, these findings cannot be adequately explained by the symmetric sensori-motor effects of prism adaptation. Taken together with the improvement of spatial neglect shown by right-deviating prisms only, the present study suggests that low level sensori-motor adaptations play a greater role in right hemisphere organisation for spatial cognition than previously thought.
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Case Reports Comparative Study Clinical Trial Controlled Clinical Trial
Interhemispheric neural summation in the split brain: effects of stimulus colour and task.
Four split-brained subjects, two subjects with agenesis of the corpus callosum, and 14 normal subjects performed two tasks requiring responses to red or green disks, briefly presented either singly in the left visual field, singly in the right visual field, or simultaneously in both visual fields. In Experiment 1, simple reaction times to these stimuli, regardless of colour, were recorded (the Go-Both Task), and found to be faster to bilateral-redundant stimulus pairs, than to single stimuli. ⋯ Redundant target stimuli produced neural summation, while stimuli pairs that included a non-target stimulus did not. These results suggest that neural summation in the acallosal or split brain involves the convergence of response-associated activation, and that redundant sensory processes are not sufficient.
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Comparative Study
Response latencies of neurons in visual areas MT and MST of monkeys with striate cortex lesions.
Cortical area, MT (middle temporal area) is specialized for the visual analysis of stimulus motion in the brain. It has been suggested [Brain 118 (1995) 1375] that motion signals reach area MT via two dissociable routes, namely a 'direct' route which bypasses primary visual cortex (area, striate cortex (V1)) and is specialized for processing 'fast' motion (defined as faster than 6 degrees/s) with a relatively short latency, and an 'indirect' route via area V1 for processing 'slow' motion (slower than 6 degrees/s) with a relatively long latency. We tested this proposal by measuring the effects of unilateral V1 lesions on the magnitudes and latencies of responses to fast- and slow-motion (depicted by random dot kinematograms (RDK) ) of single neurons in areas MT and medial superior temporal area (MST) of anaesthetized macaque monkeys. ⋯ V1 lesions led to diminished response magnitudes and increased latencies in area MT of the lesioned hemisphere, but did not selectively abolish MT responses to slow moving stimuli, or abolish long-latency responses to either slow- or fast-moving stimuli. Response magnitudes and latencies in area MST, which receives visual inputs directly from area MT and is also specialized for visual analysis of motion, were unaffected by V1 lesions (though we have shown elsewhere that directionally-selective responses in both areas were impaired by V1 lesions). Overall, the results are incompatible with the hypothesis that there are dissociable routes to MT specialized for processing separately fast and slow motion.